1. Field of the Invention
The instant disclosure relates to a manufacturing method of a porous composite film; more particularly, to a manufacturing method of a porous composite film used for separating the cathode and anode inside a lithium battery.
2. Description of Related Art
Lithium batteries are batteries that have lithium metal or lithium compounds as an anode. There are two types of lithium batteries: disposable and rechargeable. Because lithium has very high chemical reactivity, the condition for processing, storing, and using lithium is very strict. As a result, lithium batteries have long been neglected for industrial use. However, with the development in microelectronics towards the end of the 20th century, many miniaturized electronic devices are produced. Accordingly, a higher standard is demanded regarding the power source. Lithium batteries thus become more widely demanded.
The first lithium battery for use is developed by Sony in 1992. The usage of lithium batteries allows size reduction for many portable consumer electronic devices such as mobile phones, laptop computers, etc. Plus, lithium cells will provide much longer life. Since lithium batteries do not have cadmium, the lithium batteries are more environmental friendly than nickel-cadmium batteries. Other advantages of lithium batteries include portability, easy to assemble, having high energy density, and negligible amount of noise and gas. These advantages make lithium batteries a popular choice for electronic applications.
Lithium batteries include electrodes, an electrolyte, a separation film, and an outer case. The separation film is disposed between the electrodes to separate the cathode and anode. The purpose is to prevent shorting due to inadvertent chemical interactions between the electrodes. In addition, the separation film has many pores for ions to flow therethrough in forming a conductive passage.
While recharging, dendritic crystal growth of the lithium metal tends to appear on the surfaces of the electrodes. The sharp dendritic crystal structure may penetrate the separation film disposed between the electrodes and cause shorting inside the cell. The shorting of the cell results in thermal runaway and reduces its life cycle. To prevent the aforementioned condition from occurring, the separation film must be strong enough to withstand puncture.
In terms of safety in using lithium batteries, how to increase puncture resistance for the separation film in lowering the likelihood of shorting and thermal runaway is an important topic to be addressed by industrial manufacturers.